When ignorance is a bliss ?

Wrong.
What you don´t know can hurt you big time.

It's the not knowing that can do the most harm

Only in the sense that you are responsible for what you know. That applies to only a select few situations.

Everything else? You never stop learning. Always try to absorb knowledge and wisdom. :)

No what you don't know can hurt and will often hurt you eventually and often if you knew sooner you might be able to do something about it... such as early detection of cancer

That's a communist idea

not knowing hurts more in the end

Until it says: "Hello."

yes